Telecommunication systems in general and pager systems more specifically using radio broadcast message signals are presently largely employed so as to assure calling of pagers with the purpose of sending them information selectively from a central station. Such information is transmitted by means of coding schemes and predetermined message formats, such as those known under the terms POCSAG or GOLAY. In respect of the scheme POCSAG, reference may be had to the recommendation of the CCIR 584-1, Dubrovnik, 1986.
The predominant transmission coding schemes used for calling pagers have evolved from simple systems based on sequential acoustic signals towards formats based on code words made up of numerous bits and the functions offered to the user have changed in a corresponding manner from a simple acoustic warning signal to a complex multifunctional alert requiring reading of numeric or alphanumeric data on a display.
To obtain such multifunctional possibilities, pager systems and present pager-receivers include microprocessors or even microcomputers enabling them to react to information containing a large variety of coded radio-broadcast message signals. To this end known pagers are capable of receiving such signals, demodulating them, extracting therefrom dedicated call signal information and message information as such, memorizing such information and finally displaying certain selected elements of the message as transmitted.
Prior art pagers also permit the user to have at his disposition special functional possibilities such as the later repetition of messages already received and the display of the number of messages received or the time of day.
The microcomputers employed in known pagers are designed to control the operation of the receiver in order that the latter may receive radio-broadcast message signals and in order to accomplish the decoding functions of the coded message signals, memorization of given message signals, control of the display and manipulation of stored message signals in order that the various user controllable functions may be performed.
One of the major requirements of a pager is that it must handle information received in real time, otherwise there will be a risk of loss of information, for example by reason of the fact that the decoding speed is too low relative to that at which the information is received. Consequently, the operations performed by the microcomputer relative to reception, decoding, memorization and manipulation of received coded message information must be sufficiently rapid in order that the results obtained are useful for controlling the arrangement without risking loss of information. One thus must use particularly high performance microcomputers operating at a high speed.
The clock frequency necessary to attain the high operational speeds in real time can be for instance 500 kHz. Such high clock frequencies increase the feed voltage and energy consumed by the pager whilst rendering it more expensive. At the present the battery necessary for energizing current microcomputers determines to a large extent the cost, dimensions and the weight of pagers.
Additionally, such high clock frequencies and the signals which they induce in the circuits of the pager at harmonic frequencies of the clock frequency seriously disturb the processing quality which is to be expected in a good pager. Furthermore, the high consumption of energy and the physical limits of such microcomputers also bring about a limitation of functions which can be performed and offered in existing pagers.
It is also current practice to repeat two or three times the diffusion of message signals in order to guarantee that the pager for which such signals are intended receives them correctly. Known pagers thus include memory space the dimensions of which must be compatible with memorization not only of the original message signals, but also of their repetitions. The additional memory capacity which is necessitated by such repetitions increases still further the energy consumption and the cost of known pagers.
The purpose of the invention consists in providing a pager which limits or even eliminates the disadvantages of prior art pagers.